Blender 2.8 - Unwrapping VS Packing
AFAIK the unwrap function always unwrap inside the 0-1 area no matter what.

If you want to unwrap again some parts of your UV without affecting the rest, you can pin what you want to keep before unwrapping.
Just select in the UV Editor, then click UVs → Pin or press P. Don't forget to unpin when you're finished with &#9095; AltP